SuperLAME

A multithreaded MP3 encoder built on LAME, using Robert Kausch's SuperFast technique to run many libmp3lame instances in parallel and reassemble a single bit-reservoir-correct MP3 — roughly 8× faster than stock single-threaded LAME at the same quality.

It is also a small but fairly complete MP3 codec: encode, decode, wide input format support, high-quality resampling, and ID3 tagging.

What's in the box

• Encoder: LAME 3.101 beta 3 (SVN r6531) with maikmerten's "q4" quality fix (LAME bug #516).
• SuperFast MT: parallel-instance encoding + bit-reservoir repacker (ported from fre:ac/BoCA, GPL), with a self-healing fallback that guarantees valid output.
• CPU dispatch: one fat binary containing four libmp3lame builds — znver5, znver4 (AVX-512), znver3 (AVX2/FMA) and generic x86-64 (SSE2) — chosen at runtime by CPUID. (znver4/znver5 are built but unverified — no Zen 4/5 host was available to test them; znver3 and SSE2 are tested.) Intel CPUs are supported: the engines emit standard AVX-512 / AVX2+FMA+BMI2 / SSE2 instructions (Intel's too), so an Intel chip runs the matching engine — AVX-512 Intel → the AVX-512 engine, mainstream Intel → the AVX2 engine, older → SSE2. The Zen 5-tuned engine is AMD-only by design and never selected on Intel. The engines are AMD-tuned, so on Intel they run correctly but a few percent below Intel-specific tuning. (Reasoned from the ISA + dispatch logic; not yet benchmarked on a physical Intel box — Intel reports welcome.)
• Decoder: MP3 → WAV via built-in libmpg123 (--decode).
• Input: WAV (PCM 8/16/24/32-bit + 32/64-bit float), AIFF (16/24-bit), and FLAC (up to 24-bit, multithreaded decode), mono/stereo, any sample rate; - = stdin/stdout. 24-bit, float and FLAC keep full precision through LAME's float pipeline (no early truncation).
• Resampling: non-MP3 rates (e.g. 96/88.2 kHz hi-res) resampled to the nearest legal rate with r8brain (high quality, linear phase), parallelized across cores. --resample forces a rate; low bitrates auto-downsample (LAME parity).
• Tags: ID3v1 + ID3v2 (UTF-8): --tt/--ta/--tl/--ty/--tc/--tn/--tg, plus album art (--ti cover.jpg, JPEG/PNG). FLAC inputs carry their own Vorbis comments and embedded cover art through automatically (CLI flags win).
• Robustness: graceful out-of-memory refusal, hardened WAV/AIFF/MP3/FLAC parsers (input-fuzzed + tested against the IETF FLAC conformance corpus), files up to ~4 GB.

Usage

SuperLAME-1.0.2 [options] <infile> [outfile.mp3]

  -b n            CBR bitrate (kbps)
  --abr n         ABR (average) bitrate
  -V n            VBR quality 0..9 (0=best)
  --preset p      medium / standard / extreme / insane, or 8..320 (ABR)
  --resample f    output sample rate (kHz or Hz; default automatic)
  -q n            encoder quality (clamped to >=4 for CBR/ABR: bug #516)
  -m mode         a=auto s=stereo m=mono j=joint
  -t n            worker threads (0 = all cores)
  --decode        decode an MP3 to WAV
  --tt/--ta/...   ID3 tags   |   --ti cover.jpg   album art (JPEG/PNG)
  -v / --quiet    verbose / silent
  --version --about --features --longhelp --license

Run SuperLAME-1.0.2 --longhelp for the full listing.

Building

Requires clang/LLVM (for the -march=znverN intrinsics and r8brain SIMD — MSVC won't build the SIMD paths). dr_flac is vendored (dr_flac/); the other three sources are fetched (see docs/BUILDING.md):

• LAME trunk r6531
• mpg123 ≥ 1.26 (built via its CMake port)
• r8brain-free-src (header-only)

Then:

bash build/build_dispatch.sh   # compile the four prefixed libmp3lame engines
bash build/build_final.sh      # compile the frontend + link the final binary

See docs/BUILDING.md for the exact fetch/patch steps.

Notes & limits (honest)

• Speed: ~8× stock LAME in MT, but scaling plateaus at ~2 workers — the bit-reservoir repacker is a single serial stage that can't be parallelized, so more cores don't help one file. For many-core batch encoding, run one process per file.
• Memory: the whole input, its float expansion, and the output MP3 are held in RAM, so practical input is ~1–2 GB (up to ~4 GB for plain 16-bit). Larger inputs are refused with a clear message rather than crashing.
• Single-thread output is bit-identical to stock LAME; multi-thread differs only by inaudible (<-45 dB) reservoir reconciliation at chunk seams.
• Any output that needs a lower sample rate (high -V levels, low CBR/ABR, or --resample) is resampled up-front with r8brain — LAME's own per-frame resampler never runs inside a worker, which keeps MT length exactly equal to single-thread.
• FLAC limits: the bundled dr_flac decoder handles up to 24-bit; 32-bit-per- sample FLAC and a few unusual streams (mid-stream sample-rate/channel changes, extreme Rice partition orders) are refused or partially decoded with a clear message rather than producing garbage. Standard FLAC (any blocksize, predictor order, hi-res up to 384 kHz, mono/stereo) is fully supported.

Testing

tests/ contains the validation harnesses:

• regression.ps1 — validity, ST-vs-MT equivalence, and znver3-vs-SSE2 parity.
• fuzz_input.ps1 — malformed WAV/AIFF/MP3/FLAC input fuzzing.
• flac_conformance.ps1 — the IETF CELLAR flac-test-files corpus.
• odaq.ps1 — objective ST-vs-MT parity over the ODAQ reference corpus.
• sqam.ps1 / scaling.ps1 — EBU SQAM quality + core-scaling benchmarks.

See docs/ for measured results.

Support

Provided as-is, best-effort — no warranty and no support guarantee. Bug reports and PRs are welcome; please read CONTRIBUTING.md first (it lists known/intentional limits worth checking before filing). If you have a Zen 4/5 or an Intel CPU, reports are especially useful: the AVX-512 engines are built but unverified, and Intel is supported-by-design but not yet benchmarked on real hardware.

License

GPL v2 or later. This combines LAME (LGPL), mpg123 (LGPL), r8brain-free-src (MIT), dr_flac (public domain / MIT-0), and code derived from fre:ac / BoCA SuperFast (GPL v2+); the combined work is GPL. See LICENSE and THIRD-PARTY.md for full details and per-component license texts (in licenses/).